Method for forming bilayer patches

ABSTRACT

A method for injection molding thin materials (sub-millimeter) having low green strength could make certain manufacturing processes significantly more efficient yet has heretofore been unavailable. Provided herein is a method that enables injection molding of thin materials by using a mold with contact surfaces having a low surface energy release agent disposed thereon. The low surface energy release agent may be applied as a coating on a conventional mold or the mold itself or just the contact surfaces thereof may be formed of a low surface energy release material. The method finds particular applicability in making special contour patches for medical and cosmetic implants and prosthetics. A preferred approach involves injection molding a thin layer of unvulcanized material on a cold mold, injection molding a thin layer of vulcanized material on a hot mold, transferring the vulcanized layer to the unvulcanized layer on the cold mold, and removing the combined layers.

BACKGROUND

The present invention is generally directed to the manufacture ofmedical devices. More specifically, the present invention includes asystem and method for manufacturing bilayer adhesive patches that are tobe bonded to a medical device that is formed in such a manner thatpatching is required to complete the manufacture of the device.

Current manufacturing processes to make many medical implantable devicesinvolve forming thin silicone elastomer shells by dipping or molding athin layer of silicone material on a male mandrel. For example, in themanufacture of breast implants, the outer silicone membrane is formed ona male mandrel. The membrane, typically called a “shell,” is removedfrom the mandrel by cutting a small hole in the shell so that the shellcan be removed from the male mandrel without deforming or tearing theshell. Through the hole, the surrounding edges of the shell can then begrasped to stretch and peel the remainder of the shell from the malemandrel more easily. After the shell is off of the mandrel the smallcircle or hole must be patched to close the shell so as to provide fullcontainment integrity to the shell so that it may then be filled with afilling material, such as a silicone gel.

Current processes of making bilayer patches for medical and cosmeticimplants and prosthetics are more difficult, costly, and time-consumingthan they need to be. Patches for devices such as breast implants formedfrom silicone usually have a first layer that is vulcanized, which isthen applied to a second layer that is unvulcanized.

Vulcanization generally refers to the process of crosslinking thesilicone polymer based material to form a dry, non-adhering materialwith good elastomeric memory. The vulcanized layer is thin, typicallyless than 0.5 mm and preferably less than 0.2 mm. Forming thin layerswith sticky unvulcanized silicone elastomer bases is difficult andtypically done by calendering or solvent based knife-coating, withsubsequent devolatilization and vulcanization on a sheet of base plasticsuch as Teflon® (sold by DuPont), polyester or polyethylene.

The unvulcanized portion or layer of the bilayer patch, typically lessthan 0.5 mm thick, is typically applied to the vulcanized layer bycalendering unvulcanized silicone into a thin layer and then applyingthat layer to the vulcanized layer described above. Calendering refersto the process of forming a uniform thickness thin layer by pressinguncured malleable elastomer systems between rotating cylinders orrollers. It is difficult to peel thin layers off of the rollers used forcalendering without tearing or breaking the fragile thin unvulcanizedlayer. Accordingly, this process often results in a high loss factor.Alternatively, the unvulcanized layer can be applied to the vulcanizedlayer by a solvent dispersion technique and subsequently devolatilizingthe assembly before proceeding with applying the patch to the shell toclose the opening cut into the shell to remove shell from the mandrel.After the vulcanized and unvulcanized layers are joined, they aretypically supported on a thin plastic sheet.

Regardless of how the vulcanized silicone layer and unvulcanizedsilicone layer used to form the patch are combined, once combined bothsides are typically covered with a thin layer of a thermoplastic polymersuch as polyethylene. The polyethylene covered bilayer sandwich is thencut into the desired size and shape for the patch.

Consistent with current modern manufacturing procedures, the patches arethen transferred to another work area in which an assembler manuallypeels off the polyethylene coating and applies the patch to the shell byplacing in into the shell, vulcanized side away from the hole andunvulcanized side facing the hole. Vulcanization and bonding aretypically achieved by applying heat and pressure to the assembly.

Another technique that has been investigated for the manufacture of thinpatches is the use of injection molding to form the patch. Injectionmolding of silicone elastomers and plastics is common practice and awell-developed art, though it may also be used for other materials. Awide variety of products are manufactured using injection molding, whichvary greatly in their size, shape, complexity, and application.

“Green strength,” a measure of tack, deformability, elastic memory andmalleability of the unvulcanized silicone elastomer base is a relevantlimiting factor to injection molding. Moderate green strength siliconematerials typically used in forming silicone elastomer shells do noteasily lend themselves to typical mixing systems such as two rollmilling (calendering) or pumpable paste static mixer systems.

Green strength can be a good indication of processing behavior and amoderate to high green strength is desirable in processing operations inwhich it is important to maintain the integrity of a shape piece ofmaterial, particularly for the unvulcanized layer.

Thick preforms of high green strength unvulcanized silicone, typicallyformed by continuous extrusion and chopping, are commonly used inindustrial processes. However, injection molding of thin preforms havingmoderate green strength and tack is not known to have been done beforecommercially for this application on account of the adhesion between athin preform of unvulcanized silicone and common mold materials (e.g.aluminum or steel) being too strong to provide a reliable release thatpreserves the integrity of the thin preform upon removal from the mold.Injection molding of thin preforms is not commercially practical whenlosses due to the preforms being damaged, deformed, or partially stuckto the mold are too costly.

There is a need for an improved method for forming thin bilayer siliconepatches that is less expensive, less labor and time intensive, and thatreduces the loss factor of material waste. For example, the traditionalprocess of removing the polyethylene coating is tedious and transportingthe patches from one work station to the next for processing createsdelays, inefficiencies, and increased costs for labor and facilities. Itwould be desirable to provide an improved method for forming implant andprosthetic patches in which the patch assembler is able to mold thepatches on demand at a single work station. It would be especiallydesirable to provide a method for injection molding of thin preformsthat preserves the integrity of the preforms upon removal from the mold.The present invention satisfies these and other needs.

SUMMARY OF THE INVENTION

In its most general aspect, the present invention provides a process formolding patches for medical and cosmetic implants and prosthetics moreefficiently with less material and economic waste. The method providesseveral improvements over current techniques used in the art ofmanufacturing patches. For example, the method avoids problems inherentin calendering very thin materials as are required to form the patches.

In a more specific aspect, the present invention provides a way toinjection mold unvulcanized and mating vulcanized preforms of very thinmaterials of low green strength while preserving their integrity uponremoval from the mold. According to one aspect of the present invention,this is accomplished by first spraying a mold, including a conventionalmold, with a low surface energy release agent that coats the mold andfacilitates removal of the preform from it. According to another aspectof the present invention, this is accomplished by using molds in whichthe portions of the mold that make contact with the preform are formedof different materials than are conventionally used, for example, lowsurface energy plastics rather than aluminum or steel. Non-contactportions of the mold may or may not still be formed of conventionalmaterials including aluminum or steel.

In another aspect, the present invention provides a process forcombining the layers that makeup a patch, specifically the unvulcanizedlayer and the vulcanized layer. Such a bilayer assembly may be used asformed or subsequently cut into a desired patch shape. In one aspect,patches are molded on demand at a single work station, eliminating thesteps of combination through calendering or rolling squeegee technique,coating, and peeling.

Another aspect of the present invention provides a process through whichthe vulcanized layer may be transferred directly to the unvulcanizedlayer while the unvulcanized layer remains on a cold mold. The combinedlayers are together peeled off the cold mold.

In still another aspect, the present invention provides a method offorming a patch that includes: forming a layer of an unvulcanizedmaterial to a cold mold having contact surfaces comprising a low surfaceenergy release agent; applying a second layer of a vulcanized materialover the first layer of the cold molded unvulcanized material while coldmolded layer is still on the cold injection mold; allowing the secondvulcanized layer to attach to the unvulcanized layer; removing thecombined vulcanized and unvulcanized layers from the cold injectionmold; and cutting the bilayer combination into a desired shape for apatch.

According to one aspect, the combination of the unvulcanized layerattached to the vulcanized layer is less than 0.5 millimeter thick. Inanother aspect, the unvulcanized layer is less than 0.5 millimeterthick. In still another aspect, the unvulcanized material has a lowgreen strength.

In still a further aspect, the vulcanized layer is formed by calenderingand subsequent crosslinking of the polymer material. According to oneaspect, the vulcanized layer is formed by injection molding on a hotinjection mold having contact surfaces comprising a low surface energyrelease agent. According to still another aspect, the vulcanized layeris less than 0.5 millimeter thick.

In still another aspect, the contact surfaces comprising the low surfaceenergy release agent are formed by applying a coating of the low surfaceenergy release agent to the contact surfaces of the hot or coldinjection mold. According to another aspect, the contact surfaces of thehot or cold injection mold are made of a material that has a low surfaceenergy.

In a further aspect, the low surface energy release agent is afluorinated polymer. In yet a further aspect, the low surface energyrelease agent is polyvinylidene fluoride. In another aspect, the lowsurface energy release agent is polyvinylidene chloride, and in yetanother aspect, the low surface energy release agent ispoly(p-xylylene). In still another further aspect, the low surfaceenergy release agent is polytetrafluoroethylene, and in yet anotheraspect, the low surface energy release agent is a plastic.

In another aspect, the method further includes forming a label or barcode on at least one layer that will be visible on the patch. Accordingto one aspect, the label is an identifying label that may be used fortracking a manufacturing history of an implant or prosthesis to whichthe patch is applied.

In still another aspect, the method further includes forming an aperturein the patch through which a filler material may be supplied to animplant or prosthesis upon which the patch is applied, the apertureconfigured to be sealed after an implant or prosthesis is filled.

In yet another aspect, the method includes forming special contours onthe patch designed to minimize the transition between the edge of thehole in the shell and the edge of the patch.

In another aspect, the method includes forming special contours on or inthe patch to minimize the flow under pressure between the outer edge ofthe patch and the edge of the hole in the shell.

In still another aspect, the invention includes a method of forming apatch, comprising: injection molding a vulcanized polymer layer using afirst mold plate; injection molding a unvulcanized polymer layer using asecond mold plate; removing the vulcanized polymer layer from the firstmold plate; disposing the vulcanized polymer layer onto the unvulcanizedlayer while the unvulcanized layer is still on the second mold plate.compressing the vulcanized polymer layer and the unvulcanized polymerlayer until the vulcanized polymer layer adheres to the unvulcanizedlayer to form a patch; and removing the patch from the second moldplate.

In an alternative aspect, the second mold plate has a contact surfaceupon which the unvulcanized polymer layer is formed that is formed froma low surface energy material. In another aspect, the low surface energymaterial is selected from the group consisting ofpolytetrafluoroethylene, and polyvinylidene fluoride.

In yet another aspect, the second mold plate has a contact surface uponwhich the unvulcanized polymer layer is formed, the contact surfaceformed from a release agent bonded to the second mold plate. In stillanother aspect, the release agent is a low surface energy material. Inanother aspect, the release agent is a fluorinated polymer. In yetanother aspect, the release agent is selected from the group consistingof polyvinylidene fluoride, polyvinylidene chloride, andpoly(p-xylylene).

In another aspect, the invention may include applying a release coatingto a contact surface of the second mold plate upon which theunvulcanized polymer layer is formed. I an alternative aspect, therelease coating is a fluorinated polymer. In still another alternativeaspect, the release agent is selected from the group consisting ofpolyvinylidene fluoride, polyvinylidene chloride, and poly(p-xylylene).

In still another aspect, the invention includes forming a layered patch,comprising: injection molding an unvulcanized layer by molding theunvulcanized layer against a first mold having a low surface energycontact surface; forming a vulcanized layer; applying the vulcanizedlayer over the unvulcanized layer while the unvulcanized layer is stillon the first mold; adhering the vulcanized layer to the unvulcanizedlayer; removing the adhered vulcanized and unvulcanized layers from thefirst mold; and cutting the adhered vulcanized and unvulcanized layersinto a desired shape for a patch.

In another aspect, the forming vulcanized layer includes injectionmolding; in an alternative aspect forming the vulcanized layer includescalendering; and in still another aspect, forming the vulcanized layerincludes hot injections molding to cure and vulcanize the vulcanizedlayer.

In yet another aspect, injection molding the unvulcanized layer includesusing a cold injection molding process. Alternatively, injection moldingthe unvulcanized layer includes using a cold mold.

In still another aspect, the low energy surface of the mold is createdby coating a surface of the mold with low surface energy material. In analternative aspect, the low energy surface of the mold is created bybonding a release agent to a surface of the mold. In yet another aspect,the mold having a low energy surface is formed from a material having alow surface energy. In one alternative aspect, the low surface energymaterial is a fluorinated polymer; in another alternative aspect, thelow surface energy material is polyvinylidene fluoride; in anotheralternative aspect, the low surface energy material may bepolyvinylidene chloride, poly(p-xylylene), or polytetrafluoroethylene.

In yet another aspect, forming the vulcanized layer includes solventcasting.

In another aspect, injection molding the unvulcanized layer includesmolding a contour into the unvulcanized layer. In still another aspect,injection molding the unvulcanized layer includes molding forming meansfor providing an insertion point in the patch for filling an implantablesilicone breast prosthesis with fluid. In an alternative aspect, thefluid is a silicone gel.

In yet one more aspect, the present invention includes an implantablesilicone breast prosthesis manufactured using any of the aspects of theinvention set forth above. Alternatively, the present includes a patchformed using any of the aspects of the invention described previously.

Other features and advantages of the present invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating a prior art process of makingpatches.

FIG. 2 is a flow chart illustrating a process of making patches inaccordance with an embodiment of the present invention.

FIG. 3 shows a conventional injection mold, hot or cold, being coatedwith a low surface energy release agent in accordance with an embodimentof the present invention.

FIG. 4 shows an injection mold, hot or cold, having contact portionsmade of a low surface energy release material in accordance with anembodiment of the present invention.

FIG. 5 shows an injection mold, hot or cold, formed of a low surfaceenergy release material in accordance with an embodiment of the presentinvention.

FIG. 6 is a cross-sectional view showing a vulcanized layer beingapplied to a hot injection mold having a low surface energy releasematerial between the mold and the vulcanized layer.

FIG. 7 a cross-sectional view showing the vulcanized layer, afterremoval from the hot injection mold, being transferred to and appliedover an unvulcanized layer on a cold injection mold, the cold mold alsohaving a low surface energy release material.

FIG. 8 a cross-sectional view showing the vulcanized layer makingcontact with the unvulcanized layer on the cold injection mold.

FIG. 9 a cross-sectional view showing the combination of the vulcanizedlayer and the unvulcanized layer bonded together being pulled off of thecold injection mold having a low surface energy release material.

FIG. 10 is a graphical representation of one embodiment of a processused to cut the combination of the vulcanized layer and the unvulcanizedlayer into the desired shape for a patch and application of the patch tothe implant or prosthetic shell at a single work station.

FIG. 11 is a graphical flow diagram illustrating the steps of formingthe layers through injection molding, combining the layers, peeling thelayers off the mold, cutting the combined layers into a patch, andapplying the patch to the implant all being performed at a single workstation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one of its various embodiments, the present invention provides aprocess of making patches for medical and cosmetic implants andprosthetics in which the patches can be made on demand and applied tothe implant, prosthetic, or a shell thereof or precursor thereto at asingle workstation. This process reduces material losses fromcalendering and saves labor and facilities costs due to the eliminationof coating (before cutting) and peeling the coating off (after cutting)steps and the ability to concentrate the process at a singleworkstation.

Another aspect of the invention involves coating the mold material usedto injection mold the layers that form the patch with a low surfaceenergy release agent in order to facilitate removal of the layers giventhe low green strength and propensity for adhesion of thin preformmaterials. The low surface energy release agent may be, for example, afluorinated polymer, polyvinylidene fluoride, polyvinylidene chloride,poly(p-xylylene), and like compositions.

Alternatively or additionally to coating the mold material with a lowsurface energy release agent, the portions of the mold that make contactwith the preform material that forms the patch layer (“contactportions”), may themselves be made of a selected material to facilitateremoval. For example, contact portions of the mold may be made of a lowsurface energy plastic, polytetrafluoroethylene (PTFE), polyvinylidenefluoride, or like materials. Or, the entire mold may be made of one ofthese materials mentioned above to facilitate removal of thin preformswith low green strength and high adhesion.

Prior to bringing the layers together the vulcanized layer is preferablyformed by a hot injection mold while the unvulcanized layer ispreferably formed by a cold injection mold. The vulcanized layer is thenpeeled off the hot injection mold and transferred to and applied overthe unvulcanized layer on the cold injection mold. Once the layers areproperly in contact with each other the combination can be pulled fromthe cold injection mold.

The preferred patch is typically made from the combination of a layer of0.2 mm thick vulcanized silicone with a layer of 0.2 mm thickunvulcanized silicone. One desirable application for the thin preforminjection molding process is to make patches for breast implants. Forthis application, the vulcanized layer is made of a special siliconethat is so sticky it must be solvent cast into thin films or injectionmolded from solvent free paste.

The vulcanized layer may be transferred to the unvulcanized while it isstill hot from the curing process in order to promote adhesion. Theweight of the hotter vulcanized layer over the unvulcanized layer may beenough to promote bonding and adhesion between the two layers that willsecurely combine the layers with time. However, light pressure may alsobe applied to encourage the vulcanized and the unvulcanized layers tocome together to form a singular combination layer. Light pressure maybe applied, for example, by blowing air or an inert gas on the layers asthe vulcanized layer cools over the unvulcanized layer. The layers maybe allowed to rest together for up to, for example, but not limited to,twenty (20) minutes to mate until they are securely attached to eachother.

The patches and methods of producing patches described herein are suitedfor patching holes in a shell that is a precursor to an implant.Typically, a hole is intentionally created in a shell in order to moreeasily remove it from a mandrel on which it is formed. After a shell ispatched, filler material may be injected into the implant shell throughthe patch to form a completed implant ready for implantation. Or, in thecase of some implants and tissue expanders, the device may be insertedwithout filler material or with less than the final amount of fillermaterial which can be added after implantation through a port in thepatch. Common filler materials for breast implants, for example, includesilicone gels and saline solutions.

Optionally, a label may be formed on the patch during the moldingprocess. The label may be two or three dimensional. The label may beformed by painting onto a layer used to form the patch or it may beembossed on a layer through surface topography provided on the injectionmold or mandrel used to form the patch. The label may be an identifyinglabel that provides tracking information as to the manufacturing historyof the implant that may be useful in recognizing, reporting, andameliorating any issues that may arise due to particular implants. Ifeach patch receives a unique label, the label may be formed by a uniquethree-dimensional identifier (e.g. a sticker, a magnet, etc.) that isapplied to an injection mold or mandrel before the patch is formedthereon such that a three-dimensional design will be imprinted into thepatch.

To provide appropriate background to the process of patching describedherein, the process of fabricating implant shells is outlined with afocus on shells for breast implants or mammary prostheses. Breastimplant shells are generally formed on mushroom-shaped mandrels byapplying a liquid dispersion of a silicone elastomer to themushroom-head structure of the mandrel. The silicone dispersion used toform the shell may be applied by any one of several methods includingdipping or dip-molding, rotational molding (see, for example, U.S. Pat.No. 6,602,452, incorporated by reference herein in its entirety),spraying, brushing, painting, and the like.

In many situations it is preferable that the mandrel have a textured orporous surface that is transferable to the surface texture of the shell.Implants having surface texture, variable surface topography, ormicropillars have been shown to provide several post-implantationadvantages inside a patient's body that reduce post-surgicalcomplications and improve a body's acceptance and tolerance of theimplant. See, for example, European Patent No. 0416846 and EuropeanPatent No. 0710468, both of which are incorporated by reference hereinin their entirety.

Exemplary materials for mandrels include a hard resinous polymericmaterial such as epoxy or polyester (e.g. polyethylene terephthalate),polyvinylidene fluoride, polyacetal (homo or copolymer),polytetrafluoroethylene, perfluoroethylene or other fluoropolymers.Mandrels may also be formed of inert metals such as nickel or stainlesssteel, or ceramics.

In manufacturing the shell, the mandrel may be successively coated withseveral layers of the shell material dispersion with devolatilization toensure silicone is deposited in the proper thickness. After the desirednumber of layers of liquid shell material are applied to the mandrel,the mandrel coated with shell material is cured at elevated temperaturessuch as, for example, 90 to 250 degrees centigrade, depending on theparticular polymers in the dispersion, for 0.5 to 6 hours. The curedelastomer shell is then allowed to cool on the mandrel before a hole iscreated in the shell to peel it off the mandrel.

As shown in FIG. 1, in accordance with the traditional process 100 forforming patches for implant shells several steps are required which takeplace across several separate works stations. The process typicallybegins at Box 102 with the calendering of vulcanized and unvulcanizedlayers used to form the patches. The thin calendered layers are manuallypeeled off of the rollers used for calendering at Box 104. It is notuncommon for layers to be torn, damaged, or partially destroyed duringthis peeling process and accordingly the loss rate is generally higherthan desirable and contributes to the inefficiency of the traditionalprocess.

Next, the calendered layers are spread onto a thin plastic sheet at Box106. The layers are then cured with heat under pressure in Box 108.

The separately calendered and cured vulcanized and unvulcanized layersare then combined together through further calendering or by aligningthe sheets which are then combined using a rolling squeegee technique inBox 110. One or both sides of the combined layer sandwich are thencoated with a thermoplastic polymer at Box 112. The thermoplasticpolymer applied to cover the combined layer sandwich may be, forexample, polyethylene. However, other thermoplastic polymers other thanpolyethylene may also be used as a coating on the combined layersandwich.

Subsequently, the thermoplastic polymer covered sandwich of combinedlayers (one layer vulcanized, another layer unvulcanized) is cut intothe size and shape desired for an implant shell patch at Box 114. Thepatches may then be transferred to another work station in Box 116. Atthat work station, an assembler manually peels the thermoplastic polymercover off of the patch with tweezers in Box 118. Finally, with thethermoplastic cover removed, the patch is applied to a shell to form animplant using standard heat and pressure techniques at Box 120.

As shown in FIG. 2, broadly and in general terms, in accordance with theprocess 200 according to one of several embodiments of the presentinvention, an unvulcanized materials is injected into a mold assemblyhaving a contact surface covered with a low surface energy release agentat Box 202. The unvulcanized layer is then injection molded on theinjection mold at Box 204. The injection mold used may be a coldinjection mold or a hot injection mold. Typically, the mold assemblyused for injection molding the unvulcanized layer is a cold injectionmold.

At Box 206, a separate vulcanized layer is then applied over theunvulcanized layer on the mold assembly. A period of time should beallowed, and possibly also some physical pressure applied, to allow thevulcanized layer to securely attach to the unvulcanized layer on themold in 208.

Once the two layers are firmly adhered to each other upon the moldassembly used to injection mold the bottom unvulcanized layer, thecombination of layers is removed from the injection mold at Box 210.

The combination of layers is then cut into the desired size and shapefor patches at Box 212. The patches are then applied to a shell ondemand in Box 214. Each of the above steps may be performed at a singlework station.

As shown in FIG. 3, in accordance with an embodiment 300 of the presentinvention, a conventional injection mold, hot or cold, is coated with alow surface energy release agent. The conventional injection moldincludes molded part 302, molten plastic 304, raw plastic 306, clampingunit 308, mold assembly 310, injection unit 312, and injection moldingmachine 314. The enlarged view of the mold assembly 310 illustratesusing a sprayer 316 to apply a coating 318 of a low surface energyrelease agent on the surface of the mold assembly that will make contactwith the molten plastic 304 to form a molded part 302. As shown in FIG.4, the coating 318 of a low surface energy release agent has beenapplied upon all contact surfaces of the mold assembly 310.

As shown in FIG. 5, in accordance with another embodiment of the presentinvention, a conventional injection mold is modified such that the moldassembly 310 is formed entirely of a material 418 that is a low surfaceenergy release agent. Alternatively, the mold assembly 310 may be formedsuch that all contact surfaces include a material 418 that is a lowsurface energy release agent. In either of these embodiments, a coatingis not needed because the mold assembly itself, or at least the contactsurfaces thereof, are already formed of a low surface energy releasematerial.

As shown in FIG. 6, a heat curable and/or vulcanizable material isinjected into a hot injection mold assembly 311 upon which a coating 318of a low surface energy release agent has already been applied. Avulcanized layer 502 is then formed by curing and vulcanizing thevulcanizable material, such as a silicone elastomer within the hot moldassembly.

As shown in FIG. 7 and FIG. 8, the vulcanized layer 502 from the hotinjection mold assembly 311 is transferred to a cold injection moldassembly 313, upon which a coating 318 of a low surface energy releaseagent has been applied, the cold injection mold assembly 313 alreadyhaving an unvulcanized layer 504 formed thereon over which thevulcanized layer 502 is applied. The unvulcanized layer 504 was formedby injecting a suitable material, such as a silicone elastomer or itsprecursors, into a cold mold assembly. The mold assembly is then openedup, and the vulcanized layer 502 applied over the unvulcanized layer 504while the unvulcanized layer 504 remains in the mold assembly. Referringnow to FIG. 8, the thin vulcanized layer 502, conforms to the shape ofthe mold and thus also to the shape of the unvulcanized layer 504. Itwill be apparent to those skilled in the art that while the process isdescribed with reference to mold plates having a particular shape formedtherein, any shape may be molded into the various layers, or the layersmay be formed in such a manner that they are essentially flat.

As shown in FIG. 9, the vulcanized layer 502 adheres to the unvulcanizedlayer 504 on the cold injection mold 313, mating the layers to eachother. The bilayer assembly comprising vulcanized layer 502 andunvulcanized layer 503 may then be peeled off of the mold asillustrated, maintaining the integrity of the bilayer patch assembly.

Referring now to FIG. 10, upon peeling the combined layers off of themold assembly, the adhered layers 602 can be used as formed or cut intothe desired shape and size for the implant shell patches. A cutoutsection 604, or patch, of the combined layers is then transferred overto an implant shell 700 on a mandrel 710 and applied over a hole 720 inthe shell. This entire process, from cutting the adhered layers intosections to patching the hole in the implant shell on a mandrel, canoccur at a single work station 900.

FIG. 11 illustrates how all steps of the process from forming thevulcanized layer on a hot injection mold assembly as in FIG. 6, totransferring the vulcanized layer to an unvulcanized layer on a coldinjection mold assembly as in FIG. 7, to applying the vulcanized layerover the unvulcanized layer already on the cold injection mold as inFIG. 8, to peeling the adhered layers off the cold injection moldassembly as in FIG. 9, to cutting the adhered layers into patch sectionsand applying over a hole in an implant shell on a mandrel as in FIG. 10,may be performed at a single work station 900.

According to one embodiment, the injection molding process used requiresthe use of an injection molding machine, raw material, and a mold. Theprocess outline that follows assumes fabrication of a plastic part as arepresentative example but is not intended as being limited tofabrication of plastic parts.

First, if the contact surfaces of the injection mold are not composed ofa low surface energy release material or the mold is not formed of a lowsurface energy release material, the contact surfaces of the mold shouldbe coated with a low surface energy release agent. Any known manner ofcoating the mold surfaces may be used to apply the low surface energyrelease agent coating, including painting on the coating, spraying onthe coating, dipping the mold into a solution of coating, condensingvapors of the coating material onto the mold, and the like.Alternatively, the release surface may be highly polished to facilitaterelease of the material from the molds.

Next, the mixed unvulcanized silicone elastomer components are loadedinto the injection molding machine and then injected into the preheatedmold, where the silicone elastomer components are cured and vulcanizedinto the final part. The process cycle for injection molding is veryshort, typically between 2 seconds and 2 minutes.

The main stages of the injection molding process are well known in theart and include clamping, injection, and ejection. Clamping refers tothe step of securely closing and locking the two halves of the mold bythe clamping unit prior to injection of any material into the mold. Inthe injection stage, the material used to form the molded object, whichmay be a viscous fluid like material such as an uncured silicone, is fedinto the injection molding machine, and advanced towards the mold by theinjection unit. The molding material is generally is forced into thecavity of the mold under high pressure to ensure proper filling of themold cavity.

The mold plates in the injection molding machine may be heated orcooled, dependent upon the material being used and the desiredproperties of the finished molded article. In one embodiment of thepresent invention, the vulcanized layer is formed by heating the moldplate to cure and vulcanize the silicone material injected into themold. The unvulcanized layer, in contrast, is injected into a cold plateso that the silicone may cure without vulcanizing.

In the ejection stage, the molded part or article, is often ejected fromthe mold. This ejection process is not typically used in the variousembodiments of the present invention. Rather, the thin vulcanized andunvulcanized silicone layers are carefully peeled from the mold cavity.

As described previously, use of a low surface energy release materialfor construction of the mold plates, or which is applied to a standardmetal mold plate, to promote release of the molded article isparticularly advantageous when forming the thin layers of vulcanized andunvulcanized silicone of the present invention. Use of such a releaseagent allows removal of the thin layers of unvulcanized silicone havinglow green sheet from the molds while reducing the incidence of damage tothe layers during the removal step.

Further, the use of injection molding apparatus and method that providesfor easy release of the vulcanized and unvulcanized layers allows forthe combination of multiple manufacturing steps so that the entireprocess of manufacturing a patch may be carried out at a single workstation by a single operator. Such a process provides for a reduction inproduct loss due to damage, increased productivity and lowermanufacturing costs.

The present invention is not limited to the embodiments described above.Various changes and modifications can, of course, be made, withoutdeparting from the scope and spirit of the present invention. Additionaladvantages and modifications will readily occur to those skilled in theart. Accordingly, various modifications may be made without departingfrom the spirit or scope of the general inventive concept as defined bythe appended claims and their equivalents.

What is claimed is:
 1. A method of forming a patch, comprising:injection molding a vulcanized polymer layer using a first mold plate;injection molding a unvulcanized polymer layer using a second moldplate; removing the vulcanized polymer layer from the first mold plate;disposing the vulcanized polymer layer onto the unvulcanized layer whilethe unvulcanized layer is still on the second mold plate. compressingthe vulcanized polymer layer and the unvulcanized polymer layer untilthe vulcanized polymer layer adheres to the unvulcanized layer to form apatch; and removing the patch from the second mold plate.
 2. The methodof claim 1, wherein the second mold plate has a contact surface uponwhich the unvulcanized polymer layer is formed that is formed from a lowsurface energy material.
 3. The method of claim 2, wherein the lowsurface energy material is selected from the group consisting ofpolytetrafluoroethylene, and polyvinylidene fluoride.
 4. The method ofclaim 1, wherein the second mold plate has a contact surface upon whichthe unvulcanized polymer layer is formed, the contact surface formedfrom a release agent bonded to the second mold plate.
 5. The method ofclaim 4, wherein the release agent is a low surface energy material. 6.The method of claim 5, wherein the release agent is a fluorinatedpolymer.
 7. The method of claim 5, wherein the release agent is selectedfrom the group consisting of polyvinylidene fluoride, polyvinylidenechloride, and poly(p-xylylene).
 8. The method of claim 1, furthercomprising applying a release coating to a contact surface of the secondmold plate upon which the unvulcanized polymer layer is formed.
 9. Themethod of claim 8, wherein the release coating is a fluorinated polymer.10. The method of claim 8, wherein the release agent is selected fromthe group consisting of polyvinylidene fluoride, polyvinylidenechloride, and poly(p-xylylene).
 11. A patch formed by the process ofclaim
 1. 12. A method of forming a layered patch, comprising: injectionmolding an unvulcanized layer by molding the unvulcanized layer againsta first mold having a low surface energy contact surface; forming avulcanized layer; applying the vulcanized layer over the unvulcanizedlayer while the unvulcanized layer is still on the first mold; adheringthe vulcanized layer to the unvulcanized layer; removing the adheredvulcanized and unvulcanized layers from the first mold; and cutting theadhered vulcanized and unvulcanized layers into a desired shape for apatch.
 13. The method of claim 12, wherein forming the vulcanized layerincludes injection molding.
 14. The method of claim 12, wherein formingthe vulcanized layer includes calendering.
 15. The method of claim 13,wherein forming the vulcanized layer includes hot injections molding tocure and vulcanize the vulcanized layer.
 16. The method of claim 12,wherein injection molding the unvulcanized layer includes using a coldinjection molding process.
 17. The method of claim 12, wherein injectionmolding the unvulcanized layer includes using a cold mold.
 18. Themethod of claim 12, wherein the low energy surface of the mold iscreated by coating a surface of the mold with low surface energymaterial.
 19. The method of claim 12, wherein the low energy surface ofthe mold is created by bonding a release agent to a surface of the mold.20. The method of claim 12, wherein the mold having a low energy surfaceis formed from a material having a low surface energy.
 21. The method ofclaim 18, wherein the low surface energy material is a fluorinatedpolymer.
 22. The method of claim 21, wherein the low surface energymaterial is polyvinylidene fluoride.
 23. The method of claim 21, whereinthe low surface energy material is polyvinylidene chloride.
 24. Themethod of claim 21, wherein the low surface energy material ispoly(p-xylylene).
 25. The method of claim 21, wherein the low surfaceenergy material is polytetrafluoroethylene.
 26. The method of claim 12,wherein forming the vulcanized layer includes solvent casting.
 27. Theproduct formed using the process of claim
 12. 28. The method of claim12, wherein injection molding the unvulcanized layer includes molding acontour into the unvulcanized layer.
 29. The method of claim 12, whereininjection molding the unvulcanized layer includes molding forming meansfor providing an insertion point in the patch for filling an implantablesilicone breast prosthesis with fluid.
 30. The method of claim 29,wherein the fluid is a silicone gel.
 31. An implantable silicone breastprosthesis manufactured using the process of claim 12.